From MageKing17: Fix for Mantis 3502 (Flush the sexp result tree after argument evaluation to avert accidental short-circuit results)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10741 387891d4-d844-0410-90c0-e4c51a9137d3
follow-up to r10734: in the event of any SND_F flags being added in the future, this is more future-proof

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10742 387891d4-d844-0410-90c0-e4c51a9137d3
roll back r10741 pending further code review; see Mantis #3052

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10743 387891d4-d844-0410-90c0-e4c51a9137d3
fix a bug in the when-argument sexp that managed to escape detection from its original design! spotted by MageKing17, fixes Mantis #3052

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10748 387891d4-d844-0410-90c0-e4c51a9137d3
quotes can span multiple lines as well, so let's keep track of that flag (fixes Mantis #3001)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10753 387891d4-d844-0410-90c0-e4c51a9137d3
Fix mantis 3041

Allow set-skybox-model to set skybox flags (with FRED support - thanks
m!m)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10754 387891d4-d844-0410-90c0-e4c51a9137d3
Add support for voice acting in fiction viewer.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10755 387891d4-d844-0410-90c0-e4c51a9137d3
Added multiple scripting features related to messaging as requested by Axem.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10756 387891d4-d844-0410-90c0-e4c51a9137d3